1. Technical Field
The present invention relates to a method for manufacturing an electro-optic device in which an electroconductive film is removed from a substrate by applying a chemical agent onto the rotating substrate.
2. Related Art
As is generally known, an electro-optic device, such as a liquid crystal device, includes two substrates, which may be made of glass or quartz, and a liquid crystal layer disposed between the two substrates. One of the substrates has switching elements, such as thin-film transistors (hereinafter simply referred to as transistors), and pixel electrodes. The switching elements and the pixel electrodes are arranged in a matrix manner in the substrate. The other substrate has an opposing electrode. Such a structure allows the optical characteristics of the liquid crystal layer between the two substrates to change according to image signals, and thus allows an image to be displayed.
More specifically, image signals are transmitted to the plurality of pixel electrodes arranged in a matrix manner through the switching elements, such as the transistors, and voltages according to the image signals are applied to the liquid crystal layer between the pixel electrodes and the opposing electrode to change the molecular arrangement of the liquid crystal. Consequently, the transmittance of the pixels is varied, so that light passing through the pixel electrodes and the liquid crystal layer is changed according to the image signals and thus an image is displayed.
The element substrate having the transistors and the opposing substrate disposed so as to oppose the element substrate each include a thin layer, an insulating thin layer, and an electroconductive thin layer that are formed in predetermined patterns on, for example, a quartz base substrate by repeating thin-layer formation and etching for each layer.
The formation of the thin layers of the element substrate and opposing substrate uses a film-forming apparatus, such as low-pressure chemical vapor deposition (LP-CVD) apparatus or a sputtering apparatus, and the resulting thin layers are etched with an etching apparatus, such as a dry etching apparatus or a wet etching apparatus, as is generally known.
In processes of the thin layer formation and the etching, the surfaces of the quartz base substrates of the element substrate and the opposing substrate are each subjected to film formation and etching. For a sheetfed process, the rear surface of the quartz base substrate is processed generally on the stage or the like of a film-forming apparatus or an etching apparatus. In this instance, the rear surface of the quartz base substrate may be undesirably scratched or flawed by contact with the stage or the like. The rear surface of the quartz base substrate may also be scratched or flawed during transportation by contact with a carrier on which the quartz substrate is placed.
Accordingly, JP-A-2001-339069 has proposed a method for manufacturing an electro-optic device capable of preventing such a scratch or flaw caused at the rear surface of the quartz base substrate by contact during film formation or etching. In the method, an electroconductive polysilicon film is formed over the entire front and rear surfaces of the quartz base substrate before the formation of thin layers on the base substrate, and then the thin layers are formed on the polysilicon film of the front surface, followed by etching. Thus, the polysilicon film formed on the rear surface of the substrate can protect the rear surface from scratches or flaws caused by contact during film formation and etching.
The quartz base substrate placed on the stage of a film-forming apparatus or an etching apparatus is fixed on the stage with a known electrostatic chuck. This is because the electrostatic chuck can generally serve to uniformize the heat conduction in the quartz base substrate during film formation or etching and to control the temperature of the quartz base substrate. However, the base substrate is an insulator and electrostatic force does not occur between the stage and the quartz base substrate after applying a voltage.
On the other hand, the polysilicon film is electroconductive. As disclosed in the above JP-A-2001-339069, the polysilicon film formed on the rear surface of the quartz base substrate allows an electrostatic force to occur between the polysilicon film and the stage by applying a voltage. Thus, the quartz base substrate can be easily fixed on the stage by the electrostatic chuck. The polysilicon film on the rear surface of the quartz base substrate becomes unnecessary after the thin layers are formed on the front surface of the quartz base substrate, and the rear polysilicon film is finally removed by etching or the like.
In the method disclosed in the above patent document JP-A-2001-339069F, when the polysilicon film is removed from the rear surface of the quartz base substrate, a resist layer is formed over the uppermost layer of the thin layers on the front surface of the base substrate so as to cover the entirety of the thin layers in order to protect the thin layers. Then, the polysilicon film on the rear surface is removed with the quartz base substrate turned upside down by wet etching using a chemical agent, and finally the resist layer is removed with, for example, O2 plasma.
However, this technique requires the four steps of forming a resist layer, tuning the quartz substrate upside down, wet-etching the polysilicon film, and removing the resist layer, for removing the polysilicon film from the rear surface of the quartz base substrate.
Accordingly, in order to reduce the number of steps in the manufacturing process of electro-optic devices, a method is desired in which the polysilicon film can be removed from the rear surface of the base substrate through a minimized number of steps. The same applies to the case in which the polysilicon film on the front surface is removed at one time before thin layers are formed on the front surface of the base substrate.